It's unclear whether the pontiff ever rode the motorcycle, which sans the pope's signature is estimated to be worth $16,000-$20,000. But Ben Walker, head of motorcycles at auctioneer Bonhams tells Reuters: "I suspect that it will (have) very limited mileage."

"We hope to be able to do both Pope Francis and Harley-Davidson proud by raising a significant amount of money for a very worthy cause," Walker said.

A leather biker jacket also given to the pope and later signed by His Holiness will be sold separately, according to Reuters.